Five years ago, Melissa McCarthy was a jobbing stand-up, juggling time between the US comedy circuit and acting work.

Bridesmaids then unleashed a comic whirlwind that has been blowing at gale force ever since.

Fresh from starring with Sandra Bullock in The Heat, McCarthy now produces, co-writes and headlines this brash, oestrogen-fuelled road movie debut directed by husband and actor Ben Falcone.

Alas, McCarthy’s golden touch doesn’t extend to scriptwriting because Tammy is a hotch-potch of half-formed characters and ideas lacking nuance and depth.

It’s fitting that a comedy about a forty-something woman on the brink of emotional meltdown should itself be a shambles but, as a viewing experience, Falcone’s inaugural offering is more pain than gain.

The luckless heroine is Tammy (McCarthy), a dishevelled fast food restaurant worker whose car is wrecked by a wayward deer.

Fired by her boss, Tammy discovers husband Greg (Nat Faxon) enjoying a romantic meal with a neighbour (Toni Collette).

Ignoring the warnings of her mother (Allison Janney), Tammy embarks on a road trip with her profanity-spewing, hard-drinking grandmother Pearl (Susan Sarandon), who has always wanted to visit Niagara Falls.

The gung-ho ladies seek sanctuary with cousin Lenore (Kathy Bates) and her partner Susanne (Sandra Oh), and enjoy the company of cowboy Earl (Gary Cole) and his son Bobby (Mark Duplass), who takes a shine to Tammy.

“I don’t think putting two messes together is going to make an unmess,” she declares profoundly.

With each new misadventure, Tammy slowly realises she is mistress of her destiny.

Clumsily scripted and poorly paced, Tammy huffs and puffs with good intentions but barely raises a smile.

McCarthy works tirelessly but she bellyaches and gripes, without any urge to remedy her dire situation.